Poly (ε-caprolactone) (PCL) is a semi-crystalline polymer with melting point of 59˜64° C., has advantageous biocompatibility and biodegradability and is widely applied in the biomedical and medicine control fields, such as being prepared into the bandage, the suture, the drug sustained release formulation etc. In addition, due to its special properties, the mercapto-functionalized poly(ε-caprolactone) (PCLSH) also has great potential for development and hence has a wide range of applications in areas such as click chemistry, nanomaterials and biomedical sciences.
The mercapto functional poly (ε-caprolactone) is mainly synthetized by the organic catalytic method, the metal catalytic method and enzyme catalysis method. In the present study, since the thiol group itself is relatively active, it requires to be protected and deprotected during the reaction, so that the operation step becomes too cumbersome. Meanwhile, since the acid or metal catalyst used in the reaction may remain in the product, the organic catalysis and metal catalysis methods not only affect the progress of the reaction, reduces the performance of product, but limits its application in the biomedical field due to the potential toxicity herein. However, the enzyme catalysis is observed by more and more researchers due to the advantages such as mild reaction condition, high efficiency, without metal residue etc. Currently, there are various free lipases, such as porcine pancreatic lipase, pseudomonas fluorescein lipase etc., which are to be used to catalyze the ring opening polymerization of the ε-caprolactone. Compared with these traditional free enzymes, the immobilized enzymes are increasingly being used as enzyme catalyzed polymerization due to their higher stability, catalytic activity, thiol group selectivity and recyclability.
However, most of current studies on enzyme-catalyzed employ a closed reaction vessel for batch reaction, and complex separation and purification processes are required after each batch of reaction. And in the reactor, generally, the reaction solution is sufficiently contacted with the enzyme by shaking or stirring. The shear forces generated during this process can cause the immobilized enzyme to rupture or even inactivate the enzyme, so that the stability and recyclabilty of the enzyme is reduced.
Due to their good properties in mixing and heat transferring, microchannel reactors have been used in polymerization reactions in recent years and have shown great potential. Compared to conventional tank reactor, the microreactor system is relatively and is not susceptible to water, air, and other factors so as to reduce some of cumbersome measures for removing impurities. And combining an immobilized enzyme catalytic method and a micro-channel reactor to synthesize a thiol-functionalized poly(ε-caprolactone) in one step in the present invention has advantages of a simplifying process, being easy to control the reaction process, being able to control the molecular weight, green, safety, a efficiency, a fast reaction, while having a high thiol group selectivity, and a good recyclability for the immobilized enzyme.